Problem: The scale on a map is 8cm : 8km. If the distance between two cities is 32km, how far apart in cm are the two cities on the map?
Explanation: The scale means that every 8cm on the map corresponds to an actual distance of 8km. An actual distance of 32km is the same as 4 $\cdot$ 8km. The distance between the two cities on the map is 4 $\cdot$ 8cm, or 32cm.